Explanation:

The word "culture" can be defined as the beliefs, customs, arts, etc., of a particular society, group, place, or time. To identify the word that names a necessary part of "culture," we need to consider the different aspects that contribute to the definition of culture.

Customs
Customs are specific practices or behaviors that are characteristic of a particular society or group. They are an essential part of culture as they help shape the traditions, norms, and values of a community. Customs can include rituals, ceremonies, greetings, dress codes, food preferences, and social etiquette.

Education
Education plays a significant role in shaping culture. It involves the process of acquiring knowledge, skills, values, and attitudes that are passed down from one generation to another. Education helps individuals understand their cultural heritage, history, language, and traditions. It also enables them to participate actively in their society and contribute to its development.

Agriculture
While agriculture is important for the development and sustenance of a society, it is not a necessary part of the definition of culture. Agriculture refers to the practice of cultivating plants and rearing animals for food, fiber, medicinal plants, and other products used to sustain human life. Although agriculture can have a significant impact on a society's culture, it is not inherently part of the definition of culture itself.

Civility
Civility refers to the politeness, respect, and consideration shown towards others in social interactions. While civility is an important aspect of a culture's social norms and values, it is not a necessary part of the definition of culture. Civility helps maintain harmony, cooperation, and a sense of community within a society.

Conclusion
Among the given options, the word that names a necessary part of the underlined word "culture" is "customs." Customs are specific practices and behaviors that are characteristic of a particular society or group and are essential in shaping a culture's traditions, norms, and values.